The use of composites for aircraft structures has experienced a significant growth in recent years. Such structures are typically formed by curing or consolidating multiple layers of graphite/epoxy or other fiber resin composite materials into a laminate of desired configuration. As fabrication techniques have improved, it has become possible to produce large-scale composite panels having stiffeners integrally molded thereto. These stiffeners have been variously shaped, ranging from simple plate-like blades to angled structures having a T, I, L, or Z cross-sectional configuration.
Heretofore, composite structures have been principally inspected with a hand-scanning method in which a handheld yoke, carrying either through-transmission or pulse echo transducers, is manipulated by hand over the part under study. While the hand-scan methods have been successfully used to locate flaws in composite structures, they have not been entirely satisfactory. For example, since the technique is dependent upon the freehand guidance of the yoke by the operator, the technique is inherently slow and unreliable since there is no assurance that there will be 100% coverage of the part under inspection. In addition, since the operator must simultaneously manipulate the yoke and observe and analyze a displayed output of the ultrasonic transducers, it is difficult to accurately and reliably identify and locate flaws.
Another type of prior art inspection device is an ultrasonic probe that is designed to be held and manipulated by a multi-axis gantry robot. An example of such a device is described in U.S. Pat. No. 4,848,159, the parent of this application. This probe/robot combination is particularly well suited for use in a production mode to inspect large laminated structures, such as aircraft wing assemblies. Unfortunately, gantry robots of the sort necessary to manipulate an ultrasonic probe are large and cumbersome, which makes them impractical to use with a "portable" type of probe that is intended to be moved about a production facility or into the field. Further, this probe/robot combination is best suited for inspecting a laminated structure, such as a stiffener, along its entire length, as opposed to inspecting just an intermediate portion thereof. This is due, in part, to the programming used to control the gantry robot. Lastly, gantry robots are expensive to purchase and require a substantial amount of maintenance.
Another type of prior art ultrasonic inspection probe requires the use of a "mouse" or mechanical crawler to pull the probe along the part under inspection. This probe/crawler combination is better suited for use as a portable probe than the probe/robot combination discussed above. Unfortunately, however, the crawler requires the additional use of costly run-on and run-off equipment at the beginning and end of each part being inspected.
As can be appreciated from the foregoing discussion, there has developed a need for an inexpensive, portable ultrasonic inspection probe that does not require extensive auxiliary equipment for its operation. Such a portable probe could be moved about a production facility and used wherever a part that needs to be inspected is located. Further, such a portable probe could be used outside the production facility to inspect in-service parts. In addition, such a portable probe should be equally well suited for inspecting only an intermediate portion of a part, e.g., a stiffener, as well as the entire part. Also, the portable probe should be sized to allow closely spaced parts to be inspected. This invention is directed to a portable ultrasonic inspection probe that achieves these results.